We have an anchor that is guaranteed to hold, if we hold on to it.
Well, that is the faulty premise of self-salvation. It's He who holds onto us, not "we" who hold onto to Him.
"for He has said, “I will never [under any circumstances] desert you [nor give you up nor leave you without support, nor will I in any degree leave you helpless], nor will I forsake or let you down or relax My hold on you [assuredly not]!” Hebrews 13:5
"And I give them eternal life, and they will never, ever [by any means] perish; and no one will ever snatch them out of My hand." John 10:28
"My Father, who has given them to Me, is greater and mightier than all; and no one is able to snatch them out of the Father’s hand." John 10:29
No one includes "we".